The present invention relates to a liquid ejecting apparatus of an inkjet printer and so on, and more particularly, to a liquid ejecting apparatus which drives a pressure generating element using a driving signal including various kinds of ejecting pulses in an ejecting period such that dots having different sizes can be formed on a target object.
A liquid ejecting apparatus includes a liquid ejecting head which can eject liquid as a liquid droplet, and ejects various kinds of liquid from the liquid ejecting head. As a representative example of the liquid ejecting apparatus, there is an image record device of an inkjet printer and so on, which includes, for example, an inkjet record head (hereinafter, referred to as record head) as a liquid ejecting head and ejects/impacts liquid ink as an ink droplet from a nozzle orifice of the record head onto a target object such as a record sheet to form a dot and perform record. In addition, recently, the liquid ejecting apparatus applies to various kinds of manufacturing apparatuses such as a color filter manufacturing apparatus of a liquid crystal display and so on, in addition to the image record device.
In the inkjet printer (hereinafter, referred to as printer), for example, a driving signal, in which various kinds of ejecting pulses having different amounts of the ejected ink are connected to each other in series, is generated, and the ejecting pulses of the driving signal are selectively supplied to a pressure generating element such as a piezoelectric vibrator to drive the pressure generating element, thereby forming dots having different sizes on the target object such as the record sheet. For example, in a printer disclosed in JP-A-10-193587, a single driving signal is formed by a first waveform and a third waveform which are ejecting pulses for forming a middle dot and a second waveform and a fourth waveform which are ejecting pulses for forming a small dot, the waveform according to ejecting data is selected from the driving signal to be supplied to the pressure generating element, thereby forming the dot having a desired size. In addition, the printer disclosed in JP-A-10-193587 is configured by supplying all the first waveform and the third waveform to the pressure generating element to form a large dot.
Accordingly, in this kind of printer, when relatively large amount of ink is ejected onto the record sheet, such as full print, a cockring phenomenon that the record sheet is bent by the absorption of the large amount of ink may be caused. When the cockring is generated, a distance from the nozzle orifice of the record head (a nozzle formation face that is formed with the nozzle orifice) to the record surface of the record sheet (paper gap or platen gap) is reduced. Accordingly, the flight distance of the ink droplet is changed and thus record unevenness is generated or the record sheet contacts the record head and thus the record sheet is contaminated.
Since the record sheet called a dedicated sheet has an ink receiving layer and the ink is absorbed into the ink receiving layer, the cockring is not easily generated. Accordingly, when the record is performed using the dedicated sheet, the paper gap is reduced to some extent. On the contrary, when a general sheet which does not have the ink receiving layer is used, since the paper itself absorbs the ink, the cockring tends to increase. Thus, generally, when the general sheet is used in the printer, the paper gap is set to be larger than that of the dedicated sheet in consideration of looseness of the paper due to the cockring.
However, if the paper gap is large, since the flight time for ejecting and impacting the ink droplet becomes longer, the flight bending of the ink droplet is apt to be affected. As the result, a position in which a dot is formed is deviated from an adequate position and thus image quality is deteriorated. Furthermore, the ink droplet may extend in an ejecting direction by an ejecting force such that the tail thereof is separated, thereby generating a minute ink particle called satellite ink droplet. At this time, if the paper gap is large, the satellite ink droplet is not impacted onto the target object and floats in the air as mist. If the mist floats in the air, the inside of the printer is contaminated.
In order to solve the above-mentioned problems, a method of suppressing an ejecting speed (flight speed) of the ink droplet and suppressing the ink droplet from extending in the ejecting direction such that the satellite ink droplet is not generated may be considered. However, if the flight speed of the ink droplet is suppressed, since the flight time becomes longer while the vicinity of the nozzle orifice is wet or shape unevenness is apt to be affected, the flight bending becomes larger. As the result, impact accuracy is deteriorated and thus the image quality is deteriorated. Particularly, if the dedicated sheet is used, since a user requires higher image quality of the record image, the deterioration of the image quality must be suppressed, if possible.